Making cloud chambers for elementary school kids (and anyone else who would appreciate epic DIY science).

by David Ng

In about a week from now, my lab’s Science Creative Literacy Symposia fieldtrip will begin a new season in earnest. Here, I’ve got a great mix of science grad students, and creative writing MFA’s coming together to design fieldtrips, all in an attempt to highlight the fact that mixing science with creative writing isn’t such a strange thing after all.

The first session will host a Grade 5/6 class, where kids will explore the basic theme of “invisible things.” To do this, the science experiment that has been lined up involves making a DIY cloud chamber – fully capable of picking up contrails from the activity of sub-atomic particles (I know… so awesome!).

I think this is just about the perfect sort of thing to broach the subject of things that are “invisible,” and as a nice touch, I believe the grad students may go about this fieldtrip without giving the kids a heads up on what they might see (i.e. they’re aiming for that wonderful feeling of surprise and elation with discovering something unexpected – “Whoa! What was that!”).

The methodology, itself, can be found in various places on the net, but this here below is a really nicely done YouTube video on the matter, which we’ve used as the basic template.

Still, like a lot of things on YouTube, there are often details that are missing which may actually be quite important. More so, if the intent is to get a class of 11 year olds to make 12 of these things that have to work in a somewhat reliable and safe fashion.

Anyway, apart from a dark room, here are the basic supplies needed:

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There’s a couple key things that I can point out here. Firstly, the tin foil pie plate is essentially the base that will be made cold (with the dry ice), so as to create a temperature gradient, which in turn is responsible for producing an isopropanol cloud. As such, there’s a few important things it needs:

1. You need isopropanol, which is actually quite easy to get (look for the 99% rubbing alcohol in your local pharmacy). Dry ice on the other hand is sometimes tricky to get (in Canada for instance, there are official rules for its transportation).

2. It needs to be of a colour that allows you to see an isopropanol droplet cloud easily. Most videos seem to suggest something with a black surface, but this isn’t always easy to find, and possibly expensive if you need 12 of them. We’ve tried pie plates that were silver/grey (usually the most common) and red in colour (red was really difficult to observe), but the tin foil variety actually worked really well. This seems partly because it’s able to reflect the incoming flashlight, so that you can control the angle of light (just so) and in a way to best see this cloud.

3. It needs to be deep enough to encase a sufficient enough amount of dry ice, so as to more effectively maintain that cold temperature gradient. Here, we tested plates that were about 1/2 inch deep versus 1 inch deep, and the 1 inch variety worked much better. Presumably, it would also work if you just sat a thin sheet of metal right on top of a dry ice block (we were using pellets).

4. It needs to be of a material that best transfers the coldness of the dry ice to the rest of the chamber. This is why metal is often suggested, but the tin foil was just about perfect here. It’s metal, but it’s also very thin. I noted that the chamber got cold very quickly and reliably.

A second piece of equipment that needs mentioning, is the plastic cup. You can use glass, but the plastic cup works just as beautifully. Don’t forget that it has to be small enough to create a supersaturation situation, and it’s true (as the video suggested), that the smaller it is, the quicker you can see results. If possible, try to get cups without ridges so that there’s no obstructions to the observations.

Anyway, when you put it together, it’ll look a little like this:

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There’s a few key points here as well:

1. Having enough isopropanol in the system seems to be important. In this set up (with a 250ml cup) there seemed to be a big different in what we saw when there was 10ml versus 15ml of isopropanol in the system: in a nutshell, the 15ml generated a lot more visible activity (might be worth trying 20ml on the day of).

2. Concurrently, this also means you need something capable of absorbing a decent about of the alcohol, so that it’s not drippy. The video mentioned using a piece of felt, but a clipping from a “super absorbent auto sponge” worked much better (it was also a lot easier to anchor to the roof of the cup).

3. This part is IMPORTANT. The seal between the cup (after the sponge and isopropanol steps are done) and the tin foil pie plate must be completely airtight. This is why plasticine is such a great idea! As well, you should do this before any of the cooling steps, since the cooling will simply condensate water onto anything and everything, making surfaces wet and difficult to work with. I suggest putting together the cloud chamber in the following order:

(i) Construct cup + sponge + plasticine + isopropanol + tin foil pie plate” contraption. NOTE: add the isopropanol into the cup (directly on the sponge) immediately before sealing the system with plasticine. This minimizes the amount of isopropanol fumes hitting the air. In the same vein, direct handling of isopropanol is best done by an adult, and in our case, we’ll get the kids to do the sealing but will supply them with gloves (partly as a precaution, and partly because kids just like wearing gloves in a science lab) – full safety details can be found here and here (MSDS) (Thanks Dave).

(ii) Move these contraptions to your dark room (if you’re not already in it – we’ll be using a windowless lecture hall for instance).

(iii) Flip the contraptions upside down, so that the empty pie plate is now on top, AND THEN load the dry ice. (Here, of course, you’ll need to flip the whole thing upright again, so that the sponge is back on top with the dry ice at the bottom encased in the upside down pie plate – we’re going to do this with the base of an ice bucket but some sort of cold resistant matt should also work well). NOTE that dry ice should also be handled by an adult as prolonged contact can cause frostbite – see here for MSDS.

(iv) Then turn the lights off, and use your flashlight to shine a beam of light in such a way as to see that droplet cloud (looks a little like a miniature snow storm), and then, well…, then you wait. You should see something within a few minutes, but it definitely helps to be patient here.

Anyway, I’ll report back after we’ve done this, and let you know how it went with the kids. As a heads up, the creative writing portion will involve writing and acting out mini screenplays – I can’t wait!

whilst isopropanol is not the most poisonous stuff around, it is a good idea to take care against inhalation, skin & eye exposure, & ingestion. It burns well too, “Vapors may form explosive mixtures with air”.

Thanks – I tried it with my 8-yr-old son and it worked pretty well, first time. Your tips were helpful. (We used 91% isopropanol from CVS – dont know if 99% would have been any better?) I tried it again at night and got similar results – suggesting the Earth is not blocking radiation from the sun. I don’t know much about particle physics – do the solar particles spiral round in the earth’s magnetic field before hitting the atmosphere to create muons?

It would be great to get some guidance on how to divert them in a magnetic field – How many coils, what diameter, voltage etc. Or will it work with a neodymium magnet? I tried briefly but saw no effect – but not quite sure what I should be looking for….

Hi, I am one of the students helping David with the program at UBC. The cosmic radiation is coming from everywhere, and one of the sources is the sun. Some cosmic rays come from the outside our solar system! … more precisely, some particles come from outside of our solar system, hit our atmosphere, interact in various ways, and then the resulting particles enter your cloud chamber… but that might be too much detail. Some of the other particles you seen in the cloud chamber come from the ground.

I’ve not tested how strong the magnet should be but what you want to see is that tracks are curved instead of straight. Antimatter particles and matter particles will curve in different directions i.e. like how two brackets curve in opposite directions: “(” vs “)”. Here is a website to learn about it but it is not the best resource…. http://www.upscale.utoronto.ca/GeneralInterest/Harrison/AntiMatter/AntiMatter.html I’ll help David to update the information soon.

Thanks Ewan. I had thought (from watching another video) that most/all the traces were due to muons caused by solar radiation hitting our upper atmosphere. Perhaps that’s not correct – I had not realized that they could also be caused by radiation from more distant or more local sources. (Do the sources from the ground vary with local geology?)

I realize my system is not very quantitative but the fact that the results were indistinguishable at night and day sggests to me that only a small fraction of the total are coming from the sun (and that most come from other sources that don’t vary between night and day). Is that right?

We saw a lot of tracks that seemed to be horizontal or near-horizontal, which seems hard to explain if they are caused by bombardment from above. Any explanations welcome.

Even with no magnet we saw a variety of track shapes, in all directions with no obvious trend – some relatively straight, some curved or squiggly. Also the trails are constantly being distorted by the downward drift of the isopropanol droplets as they condense. If we appled a magnetic field I dont have a good sense of how easy it would be to distinguish positive versus negative particles over this background variabilty. It would be great to get a sense of what type of magnet would be needed to see an effect, and how strong the effect should be. {The website you mention, while informatige, does not contain this practical detail.)

Oh, and one more question – I had a strong impression that the trails were being created in one direction (ie they did not appear instantaneously, as might be expected if they are caused by something moving close to the speed of light). Is this a visual illusion or is it real? If real, I can imagine it could be either a slow moving particle or something to do with inhomogeneities in the isopropanol vapor that could create variable lag times in the appearance of droplets? Again, any explanation welcome!

The muons are created in the atmosphere. How much energy they have (or how fast they travel) can vary wildly. I am afraid that I do not know what speed muons the cloud chamber is capable of seeing. The cloud chamber sees more than just muons, it also sees electrons and alpha particles. Electrons will bounce around a bit more and make funny zip-zag shapes. The alpha particles will be lines that are much much thicker. Muons make longer thin straight lines. You probably see mostly a mixture of electrons and muons in your cup cloud chamber. I will look into the magnet information…..

The direction of the tracks may be hard to determine. You should note that the vapour in the container flows horizontally in one direction or another. This may make you think that the track is being made in a specific direction. This is just a thought though, it may not be true. The cosmic particles are mostly travelling vertically downwards but because of the shape of the cup cloud chamber and the position of the light, we are forcing ourselves to look at the more horizontally travelling particles. This video shows you what the cloud chamber will look like if you put radioactive source in it. Note that for the first radioactive source, the particles seem to travel towards the radioactive source but that is just the flow of the isopropanol.

David Ng is a science literacy academic and Faculty member at the University of British Columbia. He writes here and there, including humour for McSweeney's, essays for the Walrus, and blog posts for Boingboing.net. He has a molecular genetics lab full of curios and is interested in various areas of science education, communication, and outreach - particularly those where the notions of science and art intersect.

Popperfont is envisioned to be a place to share interesting, pretty things; to collect the odd thought: all categorized for use as transition pieces in talks, discussions, lectures, etc (i.e. they're striking, they're funny, they make good anecdotes). Also, this site doubles as an excuse to practice some good old science writing. It will be occasionally serious, but mostly it's all about this.

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